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Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co 4−x Mn x )Nb 2 O 9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Néel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co 4 Nb 2 O 9 , the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn 4 Nb 2 O 9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co 2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn 4 Nb 2 O 9 into the noncollinear easyplane magnetic structure, which is attributed to the large easy-plane anisotropy of Co 2+ and relative small Ising-like anisotropy of Mn 2+ . The doping effects on the Néel temperature and occupancy are also discussed.

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Based on the connotation and function Prognostics and Health Management (PHM) technology, the feasibility of PHM applied in status management of environmental testing equipment was analyzed. The status management system of environmental testing equipment based on PHM was proposed, in which the functions and prediction methods in the system were introduced.

We report experimental studies on enhancing the magnetoelectric (ME) coupling of Co 4 Nb 2 O 9 by substitution of non-magnetic metal Mg for Co. A series of single crystal Co 4-x Mg x Nb 2 O 9 (x=0, 1, 2, 3) with a single-phase corundum-type structure are synthesized by the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by Laue spots and sharp XRD peaks. Although the Né el temperature (T N ) of the Mg substituted crystals are slightly decreased from 27 K for pure Co 4 Nb 2 O 9 to 19 K and 11 K for Co 3 MgNb 2 O 9 and Co 2 Mg 2 Nb 2 O 9 , respectively, the ME coupling is double enhanced by Mg substitution when x=1. For the magnetic field (electric field) control of electric polarization (magnetization), the ME coefficient  ME of Co 3 MgNb 2 O 9 is measured to be 12.8 ps/m (13.7 ps/m). These results indicate that the Mg substituted Co 4-x Mg x Nb 2 O 9 (x=1) could serve as a potential material candidate for applications in future logic spintronics and logic devices.